The present invention is directed toward a switching array such as used in the telecommunications industry and more particularly toward a magnetic reed switching array which, through the use of a moveable electromagnet, has the ability to selectively activate or deactivate any one of a plurality of magnetic reed switches.
Switching arrays have been used for many years in various industries and in particular in the telecommunications industry for selectively opening or closing a plurality of electrical circuits. Many different types of switches have been employed including electronic switches and metallic contact switches in the form of relays, moveable conductive pins and magnetic reed switches. All, however, suffer from disadvantages.
While electronic switches are relatively fast, they are incapable of passing large signals without loss or distortion. Their uses, therefore, are somewhat limited in switching arrays used by the telecommunications industry.
Metallic contact switches offer many advantages over electronic switches including their ability to pass relatively large signals without loss or distortion. Many schemes have been proposed in an attempt to make large economical metallic contact switching arrays. The most common metallic contact switches are relays and each relay in the array must have its own winding to turn it "on" and "off" necessitating separate power leads connected to each relay. Relay switching arrays frequently employ latching relays so that the power consumed when the relays are "on" does not become excessive. In addition to a permanent or biasing magnet, these latching relays normally require two windings--one to turn the relay on and the other to turn it off. Moreover, with these prior art arrays, an additional contact must be provided on each relay to sense the state of the relay.
Another type of metallic switching array that has been employed uses an array of conductive pins which are inserted into a printed circuit board to make contact between annular rings in holes passing through the board. Stepper motors are used to position an electromechanical head in proper position above a set of holes. The electromechanical head inserts and removes the pins into and out of the desired holes. Switching times are long for this type of array because of the high degree of positioning accuracy (and subsequent small incremental movement) required by the head as well as the need to move unused pins to a repository of unconnected holes for later use. Mechanical wear also limits the life of both the pins and the holes.
Arrays have also been built utilizing magnetic reed switches. As is well known in the art, magnetic reed switches are comprised of contact pairs sealed in a glass envelope. The contacts close under the influence of an applied magnetic field. Reed switches have a usable lifetime measured in millions of operations and are available in a variety of current and voltage ratings.
One familiar use of magnetic reed switches is in the manufacture of reed relays. In such devices, a coil is wound around either one or a multiplicity of reed switches. When current is passed through the coil, the resulting magnetic field causes the reed switch to close. Adding a biasing magnet to the assembly makes a latching reed relay. The strength of the biasing magnet is insufficient to cause the reed switch to close by itself but, when current is passed through the coil, the resulting magnetic field is sufficient to cause the switch to turn on. The switches are turned off by reversing the current to the coil or by activating a second coil of opposite polarity. Prior art magnetic reed switching arrays are shown, for example, in U.S. Pat. Nos. 3,582,844; 3,928,828 and 4,019,164.
Magnetic reed relays are much faster than the other metallic switching arrays discussed above. The time it takes to set or clear a switch is in the tens of milliseconds. Furthermore, they have a much longer life than other switches. However, they suffer from the same drawback of the latching relays discussed above in that each requires its own winding to turn it "on" and "off" necessitating separate power leads connected to each relay. Moreover, an additional contact must be provided on each relay to sense the state of the relay.
At least one system has also been proposed for activating magnetic reed switches in a switching array without the use of individual electromagnets associated with each magnetic reed switch. U.S. Pat. No. 3,721,929 proposes turning magnetic reed switches on or off utilizing a magnet carried on a moveable arm which can be positioned over any selected magnetic reed switch in the array. The patent, however, proposes utilizing a moveable permanent magnet. As a result, the permanent magnet is always energized and care must be taken when moving the permanent magnet into or out of position so as not to activate or deactivate a magnetic reed switch that was not intended as the permanent magnet is moved into its desired position. The only way of accomplishing this would be to also move the permanent magnet away from the plane of the array of magnetic reed switches which obviously requires additional space and the ability to move the magnet in a third direction. Thus, the design proposed in this patent is not advantageous particularly when multiple layers of switching arrays are contemplated.